Cell Biology and Organisation: Comprehensive Study Notes

Laboratory Activity: Preparing and Examining Animal and Plant Cell Slides

  • Activity 2.1: Preparation and Examination of Animal Cells (Cheek Cells)
  • Observation Materials: Animal cell (cheek cell), methylene blue solution, distilled water, filter paper, and toothpick.
  • Apparatus: Glass slides, cover slips, light microscope, dropper, and mounting needle.
  • Procedure:
    1. Scrape the inside of the cheek gently using a blunt toothpick.
    2. Transfer the scraping into a drop of water on a clean glass slide and cover carefully with a cover slip.
    3. Stain the cheek cells with methylene blue solution using the irrigation technique.
    4. Examine the prepared slide through a light microscope.
    5. Draw the observed cheek cells and record the magnification power.
  • Activity 2.2: Preparation and Examination of Plant Cells (Onion Epidermal Cells)
  • Slide Preparation Method: Using the same irrigation technique as animal cells, but using iodine solution if necessary (though the transcript mentions methylene blue for animal cells and refers to filtering excess iodine/distilled water in step 6).
  • Procedure Detail:
    • Use a piece of filter paper to absorb excess iodine and distilled water.
    • Observe the slide through a light microscope using a low-power objective lens first, followed by a high-power objective lens.
    • Draw the epidermal cell structure and label it completely; record the magnification power.
  • Discussion Points for Observations:
    • Components observable under light microscope: Nucleus, cytoplasm, and plasma membrane (animal); Cell wall, nucleus, cytoplasm, and vacuole (plant).
    • Permanency of shape: Animal cells do not have a permanent shape; plant cells have a fixed/permanent shape due to the cell wall.
    • Specific features: Dark blue spots on cheek cells represent the nucleus stained by methylene blue.
    • Alternative plant sources: Other plants can replace onions for epidermal studies.

Components of Animal Cells and Their Functions

  • Plasma Membrane
    • Characteristics: Outer membrane surrounding the cell; made of proteins and phospholipids; thin and elastic film; partially permeable.
    • Function: Separates cell contents from the external environment; controls movement of substances into and out of the cell; allows exchange of nutrients, respiratory gases, and waste materials.
  • Centriole
    • Characteristics: Small cylindrical components that exist in pairs; made of a complex arrangement of microtubules; does not exist in plant cells.
    • Function: Forms spindle fibers during cell division in animal cells.
  • Golgi Apparatus
    • Characteristics: Consists of a stack of parallel flattened sacs coated by a single cell membrane; new membrane is added at one end while vesicles bud off the other.
    • Function: Processes, modifies, packs, and transports chemicals such as proteins, carbohydrates, and glycoproteins (the combination of carbohydrate and protein).
  • Mitochondrion (Plural: Mitochondria)
    • Characteristics: Rod-shaped or spherical; consists of two membrane layers (smooth outer membrane and folded inner membrane); contains respiratory enzymes.
    • Function: Site of energy generation through glucose oxidation during cellular respiration. Energy is released in the form of ATPATP (adenosine triphosphate) molecules.
  • Nucleus (Plural: Nuclei)
    • Characteristics: Largest cell component; spherical and compressed; enclosed in a nuclear membrane with many pores; contains chromosomes, nucleolus, and nucleoplasm.
    • Function: Controls all cell activities; contains chromosomes with DNA (deoxyribonucleic acid) which determines cell characteristics and metabolic functions.
  • Ribosome
    • Characteristics: Small, compact, spherical granules; consists of protein and RNA (ribonucleic acid); found freely in cytoplasm or attached to the rough endoplasmic reticulum.
    • Function: The site for protein synthesis.
  • Endoplasmic Reticulum (ER)
    • Characteristics: System of interconnected folded flattened sacs; continuous with the nuclear membrane.
    • Types:
      • Rough Endoplasmic Reticulum (RER): Has ribosomes attached to the surface.
      • Smooth Endoplasmic Reticulum (SER): Does not have ribosomes.
    • Function: Transport system within the cell; provides surface area for enzyme attachment and biochemical reactions. RER transports proteins; SER synthesizes and transports glycerol and lipids, and performs detoxification of drugs and metabolic by-products.
  • Lysosome
    • Characteristics: Small spherical sac enclosed in a single membrane; contains hydrolytic enzymes.
    • Function: Hydrolyses complex organic molecules (proteins, nucleic acids, lipids); breaks down bacteria and damaged cell components.
  • Cytoplasm
    • Characteristics: Jelly-like medium containing suspended cell components; contains organic compounds (proteins, lipids, carbohydrates) and inorganic compounds (potassium ions).
    • Function: Acts as the medium for biochemical reactions.

Components of Plant Cells and Their Functions

  • Cell Wall
    • Characteristics: Strong and rigid outer layer; made from cellulose fiber; fully permeable.
    • Function: Maintains the shape of the plant cell and providing mechanical support.
  • Chloroplast
    • Characteristics: Oval-shaped; consists of two membrane layers; contains chlorophyll pigments in the grana.
    • Function: Chlorophyll absorbs sunlight and converts it into chemical energy during photosynthesis.
  • Vacuole
    • Characteristics: Liquid-filled sac containing cell sap; surrounded by the tonoplast membrane; large in mature plant cells, small or absent in animal cells.
    • Composition of Cell Sap: Water, organic acids, sugars, amino acids, enzymes, mineral salts, oxygen, carbon dioxide, and metabolic by-products.
    • Function: Provides turgidity to plant cells as water is absorbed; in unicellular animals, it is involved in osmoregulation, osmosis, and excretion.

Comparison Between Animal and Plant Cells

  • Similarities: Both contain a nucleus, cytoplasm, plasma membrane, Golgi apparatus, mitochondrion, endoplasmic reticulum, and ribosomes.
  • Differences:
    • Plant Cells: Fixed shape; have a cell wall; have chloroplasts; have a large central vacuole; carbohydrate stored as starch; no centrioles.
    • Animal Cells: No fixed shape; no cell wall; no chloroplasts; vacuole is small or absent; carbohydrate stored as glycogen; have centrioles.

Living Processes in Unicellular Organisms

  • Organisms: Amoeba sp. and Paramecium sp. (Protozoans).
  • Movement:
    • Amoeba sp.: Extends pseudopodium (false feet) followed by cytoplasmic flow.
    • Paramecium sp.: Uses rhythmic cilia beats.
  • Responding to Stimuli: Both move away from adverse stimuli like chemicals, touch, or bright light.
  • Respiration: Simple diffusion of oxygen and carbon dioxide across the plasma membrane.
  • Nutrition:
    • Amoeba sp.: Phagocytosis to trap food particles; food vacuole combines with lysosome; enzymes (lysozyme) hydrolyze food; nutrients are absorbed; undigested food is discharged via movement.
    • Paramecium sp.: Cilia transfer food into the oral groove; undigested food is discharged through the anus.
  • Growth: Synthesizing new cytoplasm.
  • Excretion: Removal of carbon dioxide and ammonia by diffusion; water balance maintained by the contractile vacuole through osmoregulation.
  • Reproduction:
    • Favourable conditions: Asexual reproduction via binary fission (mitosis).
    • Unfavourable conditions: Amoeba sp. forms spores; Paramecium sp. undergoes sexual reproduction (conjugation).

Specialized Cells in Multicellular Organisms

  • Human Specialized Cells:
    • Muscle Cell: Multinuclear striated fibers; contract/relax for movement.
    • Sperm Cell: Long tail for swimming; head carries male chromosomes.
    • Nerve Cell: Long and thin; sends nerve impulses.
    • White Blood Cell: Changes shape to destroy pathogens.
    • Epithelial Cell: Thin/flat; coats organ surfaces.
    • Red Blood Cell: Biconcave disc; no nucleus; optimizes oxygen transport.
  • Plant Specialized Cells:
    • Sieve Tube Element: Long cylindrical tubes; transport organic materials.
    • Xylem Vessel: Long continuous hollow tubes; transport water and minerals.
    • Root Hair Cell: Long projection to increase surface area for absorption.
    • Palisade Mesophyll Cell: Closely arranged vertically; high chlorophyll density for photosynthesis.
    • Spongy Mesophyll Cell: Loosely arranged with air spaces for gas exchange.
    • Guard Cell: Modified epidermal cells; control stoma opening for gas exchange.

Tissue Organization and Systems

  • Human Tissues:
    • Epithelial Tissue: Covers surfaces (skin, digestive tract, trachea/cilia).
    • Muscle Tissue: Smooth (involuntary; peristalsis), Skeletal (voluntary; movement), Cardiac (involuntary; heart contraction).
    • Nerve Tissue: Neurons (cell body, dendrite, axon); sends electrical signals (nerve impulses).
    • Connective Tissue: Tendons (bone to muscle), Ligaments (bone to bone), Adipose (fat storage), Bone (frame/protection), Blood (transport/regulation), Cartilage (joint protection).
  • Plant Tissues:
    • Meristem: Apical and lateral.
    • Permanent: Dermal, Vascular (Xylem/Phloem), and Ground (Parenchyma for storage/photosynthesis, Collenchyma for support in young stems, Sclerenchyma for support in mature parts).
  • High Density of Specific Components:
    • Mitochondria: High in sperm cells, flight muscles (insects/birds), and meristem cells for energy.
    • Chloroplasts: High in palisade and spongy mesophyll for photosynthesis.
    • RER/Golgi: High in pancreatic cells and goblet cells for enzyme/mucus secretion.
    • SER/Mitochondria: High in liver cells for carbohydrate metabolism and detoxification.
  • Levels of Organisation: Cell rightarrow\\rightarrow Tissue rightarrow\\rightarrow Organ rightarrow\\rightarrow System rightarrow\\rightarrow Multicellular Organism.
  • Human Organ Systems: 11 systems including Respiratory, Digestive, Circulatory, Lymphatic, Nervous, Integumentary, Endocrine, Skeletal, Muscular, Urinary, and Reproductive.
  • Plant Systems: Shoot system (stems, leaves, flowers, fruits) and Root system.

Clinical Correlates and Failures

  • Mitochondrial Dysfunction: Can result in stunted growth, weak muscles, and vision/hearing problems.
  • Tay-Sachs Disease: A hereditary disease caused by a failure of lysosomal enzymes, leading to stunted growth and mental retardation.